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Old 14-03-2019, 15:09   #1
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Should I go AGM or Gel?

Hi all, I know similar questions have been posed muchly over the years and I've read most of the posts, but I find myself completely bamboozled by the various merits of different battery types.

So I just want to pose a very specific question:

My profile is 3-6 months of the year on the boat using the batteries quite hard every day then up to 15 months away from the boat when its on the hard and has no possibility of any charging so they may go into hard self-discharge.

Batteries are 2 x 4D and little option to swap for anything else.

Charging is primarily 150A mains charger either driven from the shore or generator. VERY rarely will I charge from the 80A alternator on the engine.


Currently I have 2 x Gel cells that have been severely abused, at one stage having been discharged down to 0V for nearly 36 months, but they came back fighting. The batteries are now 13 years old and still take a charge.

But ... I have an upcoming trip to the Bahamas and really think I should change them soon just to be prudent.

WM has Gel and AGM at more or less the same price now, so the question is Gel (which have shown themselves to be pretty bombproof) or AGM which I can charge much faster and have around 15Ah more (nominal) capacity?
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Old 14-03-2019, 15:46   #2
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Re: Should I go AGM or Gel?

Oh boy, this will be almost as good as an anchor thread!


Regardless of which you choose, proper charge regimes are necessary to not murder the battery (batteries dont die, they are murdered). So, first step I think is to educate yourself on the chare regimes for the two battery types and decide which one best fits your intended use and charge sources (alternators, solar, geneset, shore power...?).

Do some research on PSOC usage (Partial State of Charge). This is how most cruisers actually use their batteries and its a key factor in the AGM vs GEL debate. GELS are more toletant or PSOC usage than AGMs.

A con of AGMs for cruising is that they should be returned to full SOC frequently. IMHO this profile is best suited to motorized equipment, power boats, boats w gensets, or weekend warriors.

A con of gels is that they have a lower charge acceptance rate than AGMs and the charge votage must be carefully regulated. Overcharging a gel is a very effective way to murder it.

Batteries, regardless of chemistry, are NOT created equal. There is a qualitative difference between brands.

Obviously, GELs have served you well and your charge system is already set up for them, so a lot to be said for sticking with GELs. My last set of GELs also lasted about 13 years.

I expect many will say skip both for lithium, but thats not your question.
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Old 14-03-2019, 15:58   #3
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Re: Should I go AGM or Gel?

I have an AGM bank, but next bank will likely be Gel.
In truth if I could get 13 yrs out of flashlight batteries, why would I want anything else?
I mean that to say if you got 13 years, why would you want anything different?
You need Solar by the way, it works even on the hard.
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Old 14-03-2019, 16:26   #4
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Re: Should I go AGM or Gel?

My humble opinion:


You use a pair of 4D's regularly for 3-6 mos. Sounds like they are being charged & discharged regularly,which is healthy.
Then,they sit,inactive, for many months-potentially unhealthy or require proper(costly) floating equipment.


Why not install a pair of decent quality f. l.acid batteries,use them for 3-6 mos. & then give them to somebody if they will remove them.
Put a new pair in when you decide to go sailing again.


$500 fla vs $1800 AGM / Len
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Old 14-03-2019, 16:32   #5
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Re: Should I go AGM or Gel?

Gels.
In addition to the point above about PSoC use the faster charging of AGMs is dependent on having a really high capacity alternator and a high end regulator or you run the risk of frying the alternator. For the size bank you have the existing alternator is already probably close to max output during bulk charge.
If you dropped bucks for a new alternator and regulator you would save at most 30min off a full charging cycle.

For life on the hard toss out a 30w solar panel running to a cheap PWM controller to keep the batteries going dead.

I use a trolling motor for daysailing. Afterwards I toss out a 30w panel that has the battery to full in about 4 days. Total was about $150 including cabling.
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Old 14-03-2019, 16:54   #6
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Re: Should I go AGM or Gel?

Quote:
Originally Posted by duncan_ellison View Post
.

WM has Gel and AGM at more or less the same price now, so the question is Gel (which have shown themselves to be pretty bombproof) or AGM which I can charge much faster and have around 15Ah more (nominal) capacity?
I’ll let others debate opinions on battery type and focus only on your last paragraph.

Why in the world would you buy batteries at WM? They simply re-brand batteries.

I have nothing against WM and personally like their stores, however, this is analogous to buying ice cream at a shoe store. At artificially inflated prices.

Do your wallet a favor and buy batteries from a battery store.
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Old 14-03-2019, 16:57   #7
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Re: Should I go AGM or Gel?

If you are typical of many of us, you might not be so disciplined with battery charging requirements. For an expensive, but not as expensive as lithiums, check out firefly batteries, they can be quite abused and still come back. And like lithiums, they can be taken down to 80% but some have taken them down further and the batteries have survived and continued to give good service.

Video:
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Old 14-03-2019, 18:38   #8
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Re: Should I go AGM or Gel?

gel were popular 10 years ago. I have not seen them used since. they are very picky and require all charge sources to be custom set.
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Old 14-03-2019, 22:24   #9
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Re: Should I go AGM or Gel?

If Gels lasted that long for you, why would you want something else? You already have everything setup for them.

Amel is installing Gel batteries on my next boat. I would have preferred Lithium, but Gels, in my opinion, is the next best thing. After 10, or so, years, I will reevaluate.
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Old 15-03-2019, 00:49   #10
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Re: Should I go AGM or Gel?

https://www.batterystuff.com/kb/articles/battery-articles/gel-vs-agm.html
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Old 15-03-2019, 02:21   #11
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Re: Should I go AGM or Gel?

Thanks guys for the replies (so far). Belizesailor is probably right that this could turn into another anchor / guns thread, that's why I tried to frame this a specifically to my application as I could.

Although I couldn't be happier about the survivability of my current Gel batteries, I think I was really interested to know after all the hype about how great AGMs are, whether they've really turned out to be the wunderkind of the battery industry that everyone expected them to be especially on the longevity front.

I do have a well set up, temperature controlled charge system that can be set up for AGM or Gel, so keeping within the charge profile is not the issue here.

Deblen: Good thought, but the design of the boat means that only sealed batteries can work (the battery compartment is not sufficiently vented to allow the use of FLA/wet cells).

Illusion: Maybe I'm missing some thing here. I didn't find marine grade 4Ds cheaper than Defender ($$$ freight) or WM (No $$$ Freight) - Is there somewhere else I should be looking NAPA? / Walmart? / CostCo? / Sams Club? - The less I give to WM, the longer I cruise!

Belizesailor points : "Batteries, regardless of chemistry, are NOT created equal. There is a qualitative difference between brands."

Whilst there are only a relatively small number of US based battery manufacturers, there are a bunch of 'brands' clearly created by changing the decals on the cases. What's our collective view on whether these are pretty much all the same internally or whether they really do alter the chemistry/ build quality for the less premium brands?
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Old 15-03-2019, 03:19   #12
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Re: Should I go AGM or Gel?

Regarding Illusion's point: these: https://www.napaonline.com/en/p/NBP8273 appear to be made by Deka / East Penn and the case markings seem identical to the ones I already have and to the equivalent WM https://www.westmarine.com/buy/west-...07?recordNum=3

But can we deduce that internally they are likely the same plate thickness / construction etc etc. ?

Saving is around $100, but WM offer 24Mo free replacement and NAPA ony 3Mo(!).
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Old 15-03-2019, 03:35   #13
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Re: Should I go AGM or Gel?

High quality batteries were described. Until yesterday I thought AGM we're gel cell.
Sticking with what you know works well.
Solar panels on a secure hard location would certainly bring delight to either.
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Old 15-03-2019, 04:43   #14
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Re: Should I go AGM or Gel?

So .... It appears that NAPA is running a 20% discount for AAA members this month that includes batteries, so https://www.napaonline.com/en/p/NBP8273 now goes down to $532

I've a feeling that may be the way to go unless there are better suggestions.
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Old 15-03-2019, 05:29   #15
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Re: Should I go AGM or Gel?

Quote:
Originally Posted by duncan_ellison View Post
...
Although I couldn't be happier about the survivability of my current Gel batteries, I think I was really interested to know after all the hype about how great AGMs are, whether they've really turned out to be the wunderkind of the battery industry that everyone expected them to be especially on the longevity front.

...

Whilst there are only a relatively small number of US based battery manufacturers, there are a bunch of 'brands' clearly created by changing the decals on the cases. What's our collective view on whether these are pretty much all the same internally or whether they really do alter the chemistry/ build quality for the less premium brands?
AGMs are old school now, variations on lithium are the new wunderkid. Carbon foam is interesting too. However those battery techs and market are still sorting themselves out. I think in 5 years it will be sorted, prices will drop, chemistry and construction options will mature to just a few options, and it will become more of a drop in solution.

Decca/Penn mentioned above is a solid quality brand thats not wildy expense.

MainSail is a pro who does a lot of battery testing writeups. He also chimes in here occassionally. Very educational web site:

https://marinehowto.com

To the subject specifically, he has a good write up on what really constitutes a quality deep cycle battery:

https://marinehowto.com/what-is-a-deep-cycle-battery/
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